To Protect and Condition

Jan. 28, 2009
Clean Signals Need Proper Shielding and Isolation, but that’s just the starting point for proper data communication

Speed is important in processing sensor/transmitter output signals, but speed alone doesn’t necessarily give you the good signal controller input you need to ensure proper operation. Truly valid measurements are achieved sometimes only when you apply isolation and signal conditioning, but separation and protection are always a good place to start.

“For a plant to work reliably year-in and year-out, the protection of analog and digital signaling through good installation practice is a high priority,” says Alan Balcombe, global product engineering manager at Weidmüller Application Center NAFTA. “Apart from the basics of cable separation, grounding and shielding, the foundations for this protection are in high-quality signal isolation, conversion and surge protection.”

Michael Manning, vice president of engineering, Automation Systems Interconnect, suggests selecting a modular device that’s programmable. “A universal programmable signal conditioning device allows engineers to easily configure the unit to fit most applications. This gives engineers the ability to reduce inventory and cost by standardizing on one part number,” he says.

“Network engineers need to consider the performance goals and failure mode effects of their signal conditioning,” says Don Lupo, sales & marketing director at Acromag. The failure mode effect on the system means asking what happens if the sensor fails or the input/output/power wires break open or short, he explains.

“Is the signal conditioner software configurable, as well as DIP switch configurable with zero/span capabilities?” asks Tracy Lenz, senior product engineer at Wago. “Simplify by finding models that can be configured from multiple sources for multiple signal types.” This eliminates ordering wrong part numbers and minimizes on-hand stock, explains Lenz.

“Physics have not changed galvanic isolation needs, and analog signals are all around us,” says R. Coregsey, system engineer at Lutze. “We have to deal with them now and in the future.”

When relying on accurate analog signals from outdoor applications, such as wastewater plants, think about the possibility of electrical noise and interference that could affect the system, warns Mark Dietzsch, product manager at Turck. “By incorporating signal conditioners that utilize galvanic isolation, which eliminates noise and interference, the chance of disruptions to the control circuits is greatly reduced,” he explains.

Any good design inherently rejects as much noise as possible, declares Helge Hornis, Ph.D., manager, intelligent systems, at Pepperl+Fuchs. “For data networks this is typically accomplished by utilizing symmetrically designed electronics and floating signals, possibly combined with shielding,” he explains.

Signal conditioners have benefited from advances in circuit design technology, says George Tsakir, process and fluid power product manager, AutomationDirect. “They are smaller yet offer advance features such as one-touch calibration based on incoming signals and DIP-switch settable input and output ranges.”

If you’ve had problems on past applications, you probably experienced signal crosstalk, common-mode voltages, DC or AC common-mode rejection or over-range and input protection issues, explains Bill McGovern, national sales manager at Dataforth, who emphasizes all of these nightmares can be eliminated with isolated analog signal conditioners.

ETHERNET-TO-FIBEROPTICEKI-2741 converts Gigabit Ethernet networks to Gigabit fiber networks by transparently converting Ethernet signals to optic signals. It acts as a solution for applications that require wide bandwidth, EMI immunity and long-distance transmission capability. The switch supports MD/MDIX auto detection, so users don’t need to use crossover wires. Surge protection is 3,000 Vdc.Advantech, Industrial Automation Group513/742-8895
CONDITIONER line of signal conditioners includes analog converters and isolators, RTD and thermocouple converters, analog to frequency signal converters and threshold modules. The DIN-rail mountable modules, narrow as 6 mm, provide users a choice of either programmable multi-function units or single input/single output models.ASI877/650-5160
SOFTWARE CONFIGURABLE857 Series JumpFlex RTD and thermocouple modules are configured via software for applications that might be difficult to reconfigure once installed. Plugging the software tool into the RTD or thermocouple’s integrated serial port links the module to a PC via adapter cable. Both modules are configurable for fault detection/diagnostics and have an integrated DIP switch.Wago262/255-6222;
SURGE PROTECTIONCat. 5 surge protection modules connect via RJ45 sockets to protect all signal lines. They are suitable for 10BaseTx and 100BaseTx. Rated for 5 Vac, the surge protection devices have a response time of ≤5 nsec.Weidmüller800/849-9343
MINI CONDITIONERSMiniMoore multi-channel analog signal conditioners delivers up to four I/O channels in a 1-in. footprint, which equates to 0.25 in. per channel. Providing 1,000 Vrms input-to-output and channel-to-channel signal isolation, the devices can be used to isolate, convert, boost and split analog signals.Moore Industries-Int’l 818/894-7111
INTERFACE MODULEIMS interface module measures 6.2-mm wide and can be configured with a laterally mounted DIP switch. This module provides galvanic isolation and up to 2.5 kV for the input, output and power supply. It is available with signal conditioning that acts as a dead-zero to live-zero signal, or one and two-channel modules are available without signal conditioning.Turck763/553-7300
POWER HUBFieldConnex KLD2-PC-1.1.IEC Fieldbus power conditioning modules condition standard 24 Vdc supplies for fieldbus networks. They can supply up to 1 A of current to the connected field devices. They also provide the necessary impedance matching circuitry for IEC 61158-2 based networks (Foundation fieldbus, Profibus-PA).Pepperl+Fuchs330/486-0002
ANALOG SIGNAL CONDITIONERSDesigned to provide isolation for non-isolated 2-wire transmitters, 8B42 module supplies power to a current transmitter and then isolates, filters and amplifies the resulting current input signal and provides an analog voltage output. To ensure accuracy, current-to-voltage conversion takes place internally in the module. They are designed for installation in Class I, Div. 2 hazardous environments.Dataforth800/444-7644
CALIBRATED OUTPUTFC-11 is a 4-20 mA input/output signal conditioner with 1,500 Vdc isolation between input and output. It has a user-selectable factory calibration. The output is also calibrated with offset (zero) and span (full-scale) adjustments with an adjustment range of ±2% of full scale. The device eliminates ground loops or sinking/sourcing issues when interfacing to PLC analog input modules.AutomationDirect770/889-2858
ANALOG SIGNAL INTERFACEES2151 and ES2152 combination analog input/output models interface 16 dc current inputs, 16 voltage inputs and either 16 current or voltage output signals to Ethernet-enabled input signals from a rack of 8B signal conditioning modules through a DB25 port to monitor a variety of sensors, including temperature, frequency and load cells. Acromag248/295-0880
SAVE SPACESignal conditioners Christmas-tree shape provides easy access from the front. The housing comes with as many as eight poles. Input range is 0-10 V, 0-20 mA and 4-20 mA. The units are IP20-rated and DIN-rail-mountable.Lutze800/447-2371
LVDT boardModel LVDT-8A signal conditioner board offers eight channels of signal conditioning on one board, providing enhanced capability of simultaneous outputs that directly correspond to the sensed positions in a real-time environment. Use the board in factory automation environments such as machining and inspection.Acces I/O Products858/550-9559
SIMPLIFY FPGASuite of software and hardware intellectual property makes using field-programmable gate arrays (FPGAs) in measurement, control and signal processing applications easier. FPGA IPNet provides an open forum for sharing LabView FPGA IP and new hardware I/O modules for analog and digital I/O, communication buses/protocols and motion control.National Instruments                                   888/280-7645
THREE-WAY ISOLATIONiD Series signal conditioners mount on a 35-mm DIN-rail and operate 10–32 Vdc. A matching 24 Vdc/850 mA switching power supply is available. The devices have three-way isolation to 1,800 Vdc between the signal inputs, outputs and power supply and are CE-compliant.Omega Engineering203/359-1660
KEEP AWAY TRANSIENTSSTC Series data/signal line surge protection devices, in a variety of application-specific voltages and packaging configurations, prevent transient voltages from interrupting data streams or damaging vulnerable electronic equipment. Multi-stage, hybrid circuitry based on gas tubes, silicon avalanche components and resettable PTC fuses address over-voltage transients to provide high-speed, high-energy protection to network signal lines entering or leaving control panels. SolaHD800/377-4384
REDUCE WIRING TIMEAnalog system adapter for MINI MCR isolators and connectors is designed to reduce wiring time. Users plug in the system cables directly from the analog isolators or converters and into the controllers, reducing wiring and human error. The adapters have a wide range of certifications and can be used in Ex Zone 2 environments.Phoenix Contact800/888-7388
WAIT FOR THE SIGNALWV408 dc voltage/current input isolating signal conditioner and WV428 thermocouple input isolating signal conditioner can be installed directly in the Class I, Div. 2 (Groups A, B, C and D) hazardous locations. It includes Smart Power, which eliminates wasted power for low-loop-resistance loads in the current output mode; has enhanced diagnostic LEDs; comes with compact DIN-rail-mount housing; and is CE- and CSA-approved and UL-recognized.Invensys/Eurotherm703/669-1324 
GROUND OUTMSXB 078 digital I/O expansion hardware combines simultaneous operation on all channels with an isolated ground to protect your application ground currents. It provides 16 digital inputs and 16 digital outputs on an HD62 connector, with headers for alternate connectors. Eight MSXB 078 boards connected to a single DAP board provide 128 digital inputs and 128 digital outputs—all operating simultaneously and with a ground isolated from the PC.Microstar Laboratories425/453-2345